On Dec 2, 2010, at 07:55, scott brown wrote:> My first thought was that the file had low levels (before he sent > me the file), but that's definitely not the case with this file. > There are many peaks that reach 0dBFS.Live, uncompressed music often has peaks that are 4 dB higher, or more, than a typical commercial CD. Such peaks are brief, and would not really affect the total size of the FLAC file. Really, the average level is what determines whether the FLAC file ends up being smaller than 50% as it is in this case.> He sent me the original wav this morning and I loaded it into Wave > Editor on OS X. I dithered to 16 bit using MBIT+ (high/ultra > setting) and saved the 16 bit file. I did nothing else (no > normalizing or any other processing). I can't give you the 16 bit > size right now since I'm at work and the file is on my Mac at home, > but I can report back tonight.Impressive! I have read many comments that MBIT+ is the best. I've only recently licensed it myself, so I have not yet had time to form a personal opinion as to whether it is better than the dither that I have been using for years. No matter how good the dither is, though, it's still noise. The human ear and brain system cannot hear MBIT+, but FLAC is just a mathematical process. Dithering from 24-bit to 16-bit is equivalent to increasing the quantization noise by about 48 dB! It's actually quite impressive that you can add 48 dB of noise and the FLAC file only increases in size by less than 2%. Thanks for the details. I'm curious about the file size, but uncompressed WAV should be exactly as I predicted.> Whatever my process is, though, the guy who originally recorded the > file gets the same results with whatever method he uses to convert > to 16 bit on Windows. I can ask him what his 24 > 16 bit process > is. I can also just truncate the file down to 16 bit and report > back on the resulting flac file size. Would you expect that flac > file to be around the same size as the 24 bit? In my experience, > my 24/48 flac files are always substantialy bigger than my 16 bit > flac files, which is why this case confuses me...Personally, I rarely pay close attention to the exact compression. I'm happy just that FLAC is smaller and lossless. But I am still curious about the various reasons why some files turn out bigger or smaller than others. I tend to do everything in 24-bit, even final mastering, so I have not looked at 16-bit in a long while. I can say that DTS surround music disc, which is 14-bit data in 16- bit CD format, does end up with a FLAC that is almost exactly 87.5% of the WAV. This makes perfect sense, because the DTS data looks like random white noise to FLAC, and the only thing FLAC can do is compress those 2 unused bits. It's tempting to look at the 24-bit to 16-bit conversion as simply dropping 1/3 of the data, since files are based on 8-bit bytes. But one way to look at this is that FLAC deals with audio samples as if they were all 32-bit. The 16-bit samples simply have more noise. It will be interesting to see what happens with your 16-bit truncation test. I would expect that the FLAC would only get smaller, not increase in size, if all you do is truncate. Fortunately, FLAC is quite smart about bit utilization, and can even detect 16-bit samples in a 24-bit file. I don't think that's happening with your files, though, because I would expect the 24-bit FLAC to be around 33% of the 24-bit WAV if it actually only had 16- bit samples, instead of the 40% that you're seeing. But I suppose that's always possible. Brian Willoughby Sound Consulting P.S. I'm still curious where Nicholas came up with the 14% value. Is that based on decibels, bits, or some other metric I haven't thought of?
original 24/48 wav file: 264,904,968 bytes flac level 8: 105,992,780 bytes dithered 16/48 wav file:173,885,996 bytes flac level 8: 108,700,948 bytes truncated 16/48 wav file: 173,885,996 bytes flac level 8: 105,224,448 bytes RMS level of original 24 bit: -15.3dB with peaks at -0.3dB if I normalize the original file to a max of 0.0, the resulting flac file is 192,798,482 bytes. weird.... Scott On Thu, Dec 2, 2010 at 4:36 PM, Brian Willoughby <brianw at sounds.wa.com>wrote:> > On Dec 2, 2010, at 07:55, scott brown wrote: > >> My first thought was that the file had low levels (before he sent me the >> file), but that's definitely not the case with this file. There are many >> peaks that reach 0dBFS. >> > Live, uncompressed music often has peaks that are 4 dB higher, or more, > than a typical commercial CD. Such peaks are brief, and would not really > affect the total size of the FLAC file. Really, the average level is what > determines whether the FLAC file ends up being smaller than 50% as it is in > this case. > > > > He sent me the original wav this morning and I loaded it into Wave Editor >> on OS X. I dithered to 16 bit using MBIT+ (high/ultra setting) and saved >> the 16 bit file. I did nothing else (no normalizing or any other >> processing). I can't give you the 16 bit size right now since I'm at work >> and the file is on my Mac at home, but I can report back tonight. >> > > Impressive! I have read many comments that MBIT+ is the best. I've only > recently licensed it myself, so I have not yet had time to form a personal > opinion as to whether it is better than the dither that I have been using > for years. > > No matter how good the dither is, though, it's still noise. The human ear > and brain system cannot hear MBIT+, but FLAC is just a mathematical process. > Dithering from 24-bit to 16-bit is equivalent to increasing the > quantization noise by about 48 dB! It's actually quite impressive that you > can add 48 dB of noise and the FLAC file only increases in size by less than > 2%. > > Thanks for the details. I'm curious about the file size, but uncompressed > WAV should be exactly as I predicted. > > > > Whatever my process is, though, the guy who originally recorded the file >> gets the same results with whatever method he uses to convert to 16 bit on >> Windows. I can ask him what his 24 > 16 bit process is. I can also just >> truncate the file down to 16 bit and report back on the resulting flac file >> size. Would you expect that flac file to be around the same size as the 24 >> bit? In my experience, my 24/48 flac files are always substantialy bigger >> than my 16 bit flac files, which is why this case confuses me... >> > Personally, I rarely pay close attention to the exact compression. I'm > happy just that FLAC is smaller and lossless. But I am still curious about > the various reasons why some files turn out bigger or smaller than others. > I tend to do everything in 24-bit, even final mastering, so I have not > looked at 16-bit in a long while. > > I can say that DTS surround music disc, which is 14-bit data in 16-bit CD > format, does end up with a FLAC that is almost exactly 87.5% of the WAV. > This makes perfect sense, because the DTS data looks like random white > noise to FLAC, and the only thing FLAC can do is compress those 2 unused > bits. > > It's tempting to look at the 24-bit to 16-bit conversion as simply dropping > 1/3 of the data, since files are based on 8-bit bytes. But one way to look > at this is that FLAC deals with audio samples as if they were all 32-bit. > The 16-bit samples simply have more noise. It will be interesting to see > what happens with your 16-bit truncation test. I would expect that the FLAC > would only get smaller, not increase in size, if all you do is truncate. > > Fortunately, FLAC is quite smart about bit utilization, and can even detect > 16-bit samples in a 24-bit file. I don't think that's happening with your > files, though, because I would expect the 24-bit FLAC to be around 33% of > the 24-bit WAV if it actually only had 16-bit samples, instead of the 40% > that you're seeing. But I suppose that's always possible. > > Brian Willoughby > Sound Consulting > > P.S. I'm still curious where Nicholas came up with the 14% value. Is that > based on decibels, bits, or some other metric I haven't thought of? > >-------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.xiph.org/pipermail/flac/attachments/20101202/07207870/attachment.htm
On Dec 2, 2010, at 14:53, scott brown wrote:> original 24/48 wav file: 264,904,968 bytes > flac level 8: 105,992,780 bytes > > dithered 16/48 wav file:173,885,996 bytes > flac level 8: 108,700,948 bytes > > truncated 16/48 wav file: 173,885,996 bytes > flac level 8: 105,224,448 bytes > > RMS level of original 24 bit: -15.3dB with peaks at -0.3dB > > if I normalize the original file to a max of 0.0, the resulting > flac file is 192,798,482 bytes. weird....Normalizing will probably always make the FLAC larger. Of the many components of the FLAC algorithm, one is to use differential values rather than absolute, and another is to use variable-length coding (Rice coding). Quieter files have smaller differential sample values, and thus compress more. I am surprised that a mere 0.3 dB normalization would add over 80% to the FLAC size. Perhaps you missed something? Can the RMS level actually reach -0.3 dB without serious distortion? ... or did you mean -15.3 dB RMS and -0.3 dB PPM? Comparing the 24-bit WAV to the 16-bit WAV, it looks like as much as 4 MB of non-audio data is in the file. You may be looking at waveform overviews or other extra chunks in the WAV file which are usually discarded by FLAC. But this only explains a small part of the surprising numbers. One thing that stands out to me is that your original 24/48 WAV may not actually have 24-bit samples in it. I wrote a program which could detect this situation (16-bit samples in a 24-bit file), but I do not know of any other available tool to test this. It seems very suspicious that the 24-bit FLAC and truncated 16-bit FLAC are within 0.73% of each other (i.e., less than 1%). I have a suspicion that your friend is recording 24-bit files from a 16-bit A/D converter interface, or at least the software is set for 24-bit files while the interface is set to 16-bit mode. You should have the recordist double-check all settings. A mistake here would easily explain the strange FLAC compression ratios. Brian Willoughby Sound Consulting